/**
 *    Copyright 2009-2017 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.scripting.xmltags;

/**用于描述动态sql中if标签的内容，XMLLanguageDriver在解析Mapper SQL配置生成SqlSource时，会对动态sql中的if标签进行解析，将if标签转换为IfSqlNode对象
 *
 * @author Clinton Begin
 */
public class IfSqlNode implements SqlNode {
	
	/**用于解析OGNL表达式
	 * 
	 */
	private final ExpressionEvaluator evaluator;
	/**保存if标签的test属性内容
	 * 
	 */
	private final String test;
	/**保存if标签的sql内容
	 * 
	 */
	private final SqlNode contents;

	public IfSqlNode(SqlNode contents, String test) {
		this.test = test;
		this.contents = contents;
		this.evaluator = new ExpressionEvaluator();
	}

	@Override
	public boolean apply(DynamicContext context) {
		// 如果OGNL表达式为true，才会执行if标签中sql内容对应的SqlNode的apply方法，这样就实现了只有当if标签test属性表达式值为true时，才会追加if标签中配置的sql信息
		if (evaluator.evaluateBoolean(test, context.getBindings())) {
			contents.apply(context);
			return true;
		}
		return false;
	}

}
